Like the others mentioned, you wont really know what your dealing with until he fully settles in as a gelding. My coming 8 year old (in my avatar) was only gelded last year, and had been used as a breeding stallion before that, so I had a lot of concern about putting him with my other horses - especially my young colt. It had been close to 6 months he had been gelded when I got him. I got lucky, he did fine with my horses, and seemed to have no "studdy" behaviors retained, other than initially he did try to mount my pony when she was in heat - so we seperated her out when she was cycling, until the last few months he has stopped doing it (though she has continued to cycle this winter). There is always a chance a horse gelded that late will retain some studdy habits, sometimes for a long time, sometimes forever, and you have to learn to work around it. You might not ever be able to turn him out with your herd. You might just have to give it some time. It's really a wait and see kind of thing.